Suppressive effects on motion discrimination induced by transient flankers are reduced by perceptual learning

We investigated spatial suppression of a drifting Gabor target of 0.5 c/° induced by adjacent and iso-oriented stationary Gabors (flankers) whose spatial frequency differed by ±1 and ±2 octaves to that of the drifting target. Stimuli (target and flankers) were presented for 33 ms. Results showed greater spatial suppression when the spatial frequency of the stationary but transient flanking Gabors was either equal or 1-2 octaves lower than when it was 1-2 octaves higher than the target's spatial frequency. This asymmetry was evident only for the drifting target, but not for the stationary target. In addition, we investigated whether perceptual learning (PL) reduced the spatial suppression induced by the flankers. We found that PL increased contrast sensitivity for the target, but only when it was reduced by the lateral masking flankers, and its effect did not transfer to an isolated drifting target of equal or higher spatial frequency. These results suggest that PL selectively affects suppressive interactions rather than contrast gain. We suggest that the suppressive effect of low spatial frequency flankers and the lack of suppression with high spatial frequency flankers may reflect two complementary phenomena: camouflage by the transient flankers (i.e., context) and breaking of camouflage by form-motion segmentation. Camouflage may result because both target and flankers activate the motion (magnocellular) system. Breaking of camouflage instead may occur when target and flankers' spatial frequency are more suitable for quasi-independent activation of the form system (by the flankers) and the motion system (by the target).